Chitin (poly-N-acetyl-D-glucosamine) is a polysaccharide widely distributed in nature and is a major component of the cell wall of various fungi as well as the shell of insects and crustaceans. Chitin has been extracted and purified from its various sources and has been formed into potentially useful articles such as fibers for medical sutures. Chitin-based fibers having both high tensile strength and high modulus of elasticity prepared directly without post fiber treatment would be highly desirable.
Previous work to provide high strength chitin fibers has included the after-treatment of wet-spun chitin fibers in a second coagulation bath as described in U.S. Pat. No. 4,431,601 or by drawing the fiber as described in Japanese Patent Pub. (Kokai) No. 58-214,513.
Methods to produce chitosan (poly-D-glycosamine) and chitin acetate (poly-N-acetyl-O-acetyl-D-glycosamine) are known and methods for spinning chitosan and chitin acetate into fibers are described in Japanese Patent Pubs. (Kokai) No. 56-106901 and No. 53-126063, respectively.
In the polysaccharide art, optically anisotropic spinning solutions from cellulose and cellulose acetate have been disclosed. An object in the cellulose art was to provide a concentrated solution of highly polymerized cellulose triacetate as well as a large degree of acetate substitutions in order to produce high strength fibers as described in U.S. Pat. No. 4,464,323.
It has now been discovered that by forming a fiber from the mixed derivative of chitin or chitosan acetate/formate that significantly higher tenacity can be obtained. Higher tenacity chitin acetate fibers are obtainable by lowering the degree of substitution. This is completely unexpected in light of U.S. Pat. No. 4,464,323.